Vehicle-Mounted radio wave radar

ABSTRACT

An antenna base, a control circuit section, and a high-frequency circuit section are enclosed in an inner space defined by a housing and a radome. Inside this inner space, the control circuit section and the high-frequency circuit section are surrounded by the antenna base and the housing. A circuit GND common to the control circuit section and the high-frequency circuit section is electrically connected to the antenna base and the housing, and it is connected to a body GND through only capacitive impedance.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a vehicle-mounted radio waveradar for detecting a variable such as a distance or relative speedbetween a host vehicle (radar-loaded vehicle) and a target in front ofthe host vehicle.

[0003] 2. Description of the Related Art

[0004] There is known a vehicle-mounted radio wave radar for detecting avariable such as a distance or relative speed between a host vehicle anda target, e.g., another vehicle or an obstacle, in front of the hostvehicle by using radio waves of the millimeter-wave (EHF) band (60-77GHz) in which radio wave beams are less attenuated even in foggy orother bad weather and are able to propagate over a long distance.

[0005] Examples of such a vehicle-mounted radio wave radar are disclosedin JP, A, 10-79616 and 10-261917.

[0006] In the former JP, A, 10-79616, a radome and a housing areemployed to provide a structure for enclosing, e.g., an antenna, ahigh-frequency circuit section for processing a transmitted/receivedsignal in the same high-frequency range as the transmitted/receivedsignal, and a control circuit section for processing thetransmitted/received signal in a relatively low-frequency range andperforming other required processing. With this structure, the antennais covered from front by the radome made of a material, such as a resin,which is transparent to electromagnetic waves of the millimeter-waveband with high efficiency, and the remaining part is covered by thehousing. The latter JP, A, 10-261917 employs a structure that anantenna, a high-frequency circuit section and a control circuit sectionare stacked in a housing in this order and fixed to the housing byscrews or the likes, and that a ground potential metallic layer isprovided between the high-frequency circuit section and the controlcircuit section.

[0007] In the conventional vehicle-mounted radio wave radars describedabove, ground terminals of the components, i.e., the control circuitsection and the high-frequency circuit section, are connected to aground terminal of a battery remote from the position at which the radaris attached to a vehicle body. The ground terminal of the battery isconnected to the vehicle body for grounding. Accordingly, impedance of acertain value depending on wires, body, and other vehicle parts existsbetween the ground terminals of the control circuit section and thehigh-frequency circuit section, the ground terminal of the battery, andthe vicinity of the position at which the radar is attached to thevehicle body.

[0008] The presence of such impedance generates a noise loop throughthose vehicle parts and may deteriorate the performance of thevehicle-mounted radio wave radar because useless noises and staticelectricity are applied to the vehicle-mounted radio wave radar.

[0009] Further, when the components of the vehicle-mounted radio waveradar are stacked in a housing and fixed to the housing by screws or thelikes as disclosed in the latter JP, A, 10-261917, the assembly work isdifficult to implement because the housing is usually designed to havethe least necessary size just enough to accommodate the components for asize reduction.

SUMMARY OF THE INVENTION

[0010] Accordingly, it is an object of the present invention to providea vehicle-mounted radio wave radar which can restrain a deterioration ofthe performance caused by adverse effects of useless noises and staticelectricity. Another object of the present invention is to facilitateassembly work of the vehicle-mounted radio wave radar.

[0011] To achieve the above object, according to a first aspect of thepresent invention, a vehicle-mounted radio wave radar comprises atransmitting/receiving unit for transmitting and receiving a radiosignal; a signal processing unit for processing the radio signaltransmitted and received by the transmitting/receiving unit; anelectrically conductive housing for accomodating the signal processingunit therein; an electrically conductive support plate supporting thetransmitting/receiving unit and disposed so as to close an opening ofthe electrically conductive housing; and an insulating member forelectrically isolating the electrically conductive housing and a vehiclebody from each other. Ground lines of the transmitting/receiving unitand the signal processing unit are electrically connected to theelectrically conductive housing and the electrically conductive supportplate.

[0012] According to the first aspect, the ground lines of thetransmitting/receiving unit and the signal processing unit, which areelectronic parts constituting the vehicle-mounted radio wave radar, areelectrically connected to the electrically conductive housing and theelectrically conductive support plate. Also, the electrically conductivehousing is electrically isolated from the vehicle body by the insulatingmember. Therefore, the transmitting/-receiving unit and the signalprocessing unit are electrically shielded by the ground potential ofthemselves, and hence adverse effects of useless noises and staticelectricity are reduced.

[0013] Also, according to a second aspect of the present invention, avehicle-mounted radio wave radar comprises a transmitting/receiving unitfor transmitting and receiving a radio signal; a signal processing unitfor processing the radio signal transmitted and received by thetransmitting/-receiving unit; an electrically conductive housing foraccommodating the signal processing unit therein; an electricallyconductive support plate supporting the transmitting/receiving unit anddisposed so as to close an opening of the electrically conductivehousing; and a capacitive device having one end connected to theelectrically conductive housing and the other end connected to thevicinity of a position at which the vehicle-mounted radio wave radar isattached to a vehicle body, the capacitive device electricallyconnecting the electrically conductive housing and the vehicle body toeach other through capacitive impedance. Ground lines of thetransmitting/receiving unit and the signal processing unit areelectrically connected to the electrically conductive housing and theelectrically conductive support plate.

[0014] According to the second aspect, the ground lines of thetransmitting/receiving unit and the signal processing unit, which areelectronic parts constituting the vehicle-mounted radio wave radar, areelectrically connected to the electrically conductive housing and theelectrically conductive support plate. Also, the electrically conductivehousing is electrically connected to the vehicle body through thecapacitive device. Therefore, the transmitting/receiving unit and thesignal processing unit are electrically shielded by the ground potentialof themselves. In addition, a surge, which is produced by thetransmitting/receiving unit and the signal processing unit due to apotential difference between the ground potential of themselves and theground potential in the vicinity of the position at which the radar isattached to a vehicle body, is absorbed by the capacitive impedance ofthe capacitive device. As a result, adverse effects of useless noisesand static electricity are further reduced in comparison with the radaraccording to the first aspect.

[0015] Further, according to a third aspect of the present invention, avehicle-mounted radio wave radar comprises a transmitting/receiving unitfor transmitting and receiving a radio signal; a signal processing unitfor processing the radio signal transmitted and received by thetransmitting/-receiving unit; an electrically conductive inner housingfor accommodating the signal processing unit therein; an electricallyconductive support plate supporting the transmitting/receiving unit anddisposed so as to close an opening of the electrically conductivehousing; an electrically conductive outer casing for accommodating theelectrically conductive inner housing therein; and a capacitive devicehaving one end connected to the electrically conductive inner housingand the other end connected to the electrically conductive outer casing,the capacitive impedance device electrically connecting the electricallyconductive inner housing and the electrically conductive outer casing toeach other through capacitive impedance. Ground lines of thetransmitting/receiving unit and the signal processing unit areelectrically connected to the electrically conductive inner housing andthe electrically conductive support plate, and the electricallyconductive outer casing is electrically connected to a vehicle body.

[0016] According to the third aspect, the ground lines of thetransmitting/receiving unit and the signal processing unit, which areelectronic parts constituting the vehicle-mounted radio wave radar, areelectrically connected to the electrically conductive inner housing andthe electrically conductive support plate. Also, the electricallyconductive inner housing is electrically connected to the electricallyconductive outer casing that is in turn electrically connected to thevehicle body through the capacitive device. As a result, as with thesecond aspect, adverse effects of useless noises and static electricityare further reduced in comparison with the radar according to the firstaspect.

[0017] Moreover, according to a fourth aspect of the present invention,a vehicle-mounted radio wave radar comprises a transmitting/receivingunit for transmitting and receiving a radio signal;

[0018] a signal processing unit for processing the radio signaltransmitted and received by the transmitting/-receiving unit; anelectrically conductive housing for accommodating the signal processingunit therein; and an electrically conductive support plate supportingthe transmitting/receiving unit and disposed so as to close an openingof the electrically conductive housing. The electrically conductivehousing is electrically connected to a vehicle body, and impedancebetween a ground terminal of the signal processing unit and theelectrically conductive housing is kept small to such an extent that apotential difference produced therebetween is negligible.

[0019] According to the fourth aspect, the electrically conductivehousing is electrically connected to the vehicle body so as to keep theimpedance between the ground terminal of the signal processing unit andthe electrically conductive housing small to such an extent that thepotential difference produced therebetween is negligible. As a result,the generation of useless noises and static electricity attributable toa noise loop can be restrained.

[0020] Additionally, in the vehicle-mounted radio wave radar accordingto any of the above aspects of the present invention, the radar may beassembled by placing the signal processing unit within the electricallyconductive housing while a biasing unit is arranged on the side (sameside as the opening of the electrically conductive housing) above thesignal processing unit and/or the side (same side as the bottom of theelectrically conductive housing) below the signal processing unit; andarranging the electrically conductive support plate supporting thetransmitting/-receiving the in the opening of the electricallyconductive housing, in which the signal processing unit is placed, insuch a manner that the signal processing unit is fixedly positionedwithin the electrically conductive housing by a biasing force imposedfrom the biasing unit.

[0021] With those features, the signal processing unit can be fixedlypositioned within the electrically conductive housing with no need ofusing screws or the likes, and the assembly work can be facilitated.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022]FIG. 1 is a block diagram showing the functional configuration ofa vehicle-mounted radio wave radar according to one embodiment of thepresent invention;

[0023]FIG. 2 is a representation for explaining a situation in which thevehicle-mounted radio wave radar shown in FIG. 1 operates.

[0024]FIGS. 3A, 3B and 3C show examples of the structure of thevehicle-mounted radio wave radar shown in FIG. 1 with attention focusedon the relationship between a circuit GND (ground), which is a commonGND to a control circuit section and a high-frequency circuit section,and a body GND;

[0025]FIG. 4 is a sectional view of the vehicle-mounted radio wave radarshown in FIG. 1 in a state where it is attached to a vehicle body;

[0026]FIG. 5 is a schematic view, showing another assembly method, ofthe structure of the vehicle-mounted radio wave radar shown in FIG. 1;and

[0027]FIG. 6 is an external view showing an appearance of thevehicle-mounted radio wave radar shown in FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0028] One preferred embodiment of the present invention will bedescribed below.

[0029]FIG. 1 shows the functional configuration of a vehicle-mountedradio wave radar according to one embodiment of the present invention.

[0030] Referring to FIG. 1, a signal processing and control circuit 18performs rectangular wave modulation of an oscillation signal, which issupplied from an oscillator 9, through a rectangular wave modulatingcircuit 15. A transmitting antenna 4 is energized by the modulatedoscillation signal to emit electromagnetic waves forward. Also, as shownin FIG. 2, the electromagnetic waves reflected by a preceding vehicle 7is received by a receiving antenna 5 and supplied to the signalprocessing and control circuit 18 through a mixer 8, an amplifier 11, aselector switch 12, and low-pass filters 13, 14. The signal processingand control circuit 18 computes a variable such as a relative speedV2-V1 or a vehicle-to-vehicle distance D1 between a host (radar-loaded)vehicle 23 and the preceding vehicle 7 going ahead of the host vehicle23 based on the received signals and output signals from an internal yawrate sensor 17 and various external sensors. Results of the computation,etc. are informed to an external device 20 as appropriate.

[0031] In the above arrangement, the signal processing and controlcircuit 18, the rectangular wave modulating circuit 15, the amplifier11, the selector switch 12, the low-pass filters 13, 14, and the yawrate sensor 17 constitute a control circuit section 10. Also, theoscillator 9 and the mixer 8 constitute a high-frequency circuit section6. Further, in FIG. 1, numeral 1 denotes a redome made of a resinallowing electromagnetic waves of the millimeter-wave band to passthrough it without attenuation. Numeral 2 denotes a housing, and 3denotes an antenna base for the antennas 4, 5.

[0032] A description will be next made of the structure of thevehicle-mounted radio wave radar according to the embodiment whileprimarily focusing on the relationship between a circuit GND (ground),which is a common GND to both the control circuit section 10 and thehigh-frequency circuit section 6, and a body GND.

[0033]FIGS. 3A, 3B and 3C show examples of the structure of thevehicle-mounted radio wave radar shown in FIG. 1 with attention focusedon the relationship between a circuit GND 27, which has a groundpotential common to both the control circuit section 10 and thehigh-frequency circuit section 6, and a body GND 26 which has a groundpotential in the vicinity of the position at which the vehicle-mountedradio wave radar is attached to a vehicle body. As shown, a positivepower supply terminal of the vehicle-mounted radio wave radar isconnected to a positive terminal of a battery, whereas the circuit GND27 and the body GND 26 are connected to a negative terminal of thebattery. Also, in FIG. 3, Z1 represents impedance between the positivepower supply terminal of the vehicle-mounted radio wave radar, Z2represents impedance between the circuit GND 27 and the negativeterminal of the battery, and Z3 represents impedance between the bodyGND 26 and the negative terminal of the battery. Additionally, numeral29 denotes a filter.

[0034]FIG. 3A shows a first example of the structure of thevehicle-mounted radio wave radar.

[0035] In the first example of the structure shown in FIG. 3A, thehigh-frequency circuit section 6 is entirely covered by a metal, andthis metal is connected to a ground line of the high-frequency circuitsection 6. The transmitting antenna 4 and the receiving antenna 5 aremounted on the metal-made antenna base 3. The housing 2 is anelectrically conductive one. An outer wall surface of the housing 2 ishowever covered by an insulator 30 in its portion attached to thevehicle body. Also, the antenna base 3, the control circuit section 10,and the high-frequency circuit section 6 are arranged in a space definedby the housing 2 and the antenna base 3. Furthermore, the antenna base 3is covered by a radome 1.

[0036] The circuit GND 27 common to both the control circuit section 10and the high-frequency circuit section 6 is electrically connected tothe antenna base 3 and the housing 2. The circuit GND 27 is alsoconnected to the body GND 26 through capacitive impedance 31 in the formof, e.g., a capacitor. A resistance connected to the capacitor inparallel (for protection of the capacitor) can be provided in asufficient value by the impedance of the capacitor itself.

[0037] With the first example of the structure shown in FIG. 3A, thecircuit GND 27, which has a ground potential common to both the controlcircuit section 10 and the high-frequency circuit section 6, iselectrically connected to the housing 2 and the antenna base 3. Further,the housing 2 is electrically isolated from the body GND 26 by theinsulator 30 except for a portion where the housing 2 is connected thebody GND 26 through the capacitive impedance 31. Accordingly, thecontrol circuit section 10 and the high-frequency circuit section 6 areelectrically shielded by the ground potential of themselves. Also, sincethe circuit GND 27 and the body GND 26 are electrically connected toeach other through the capacitive impedance 31, a surge generatedbetween the circuit GND 27 and the body GND 26 is absorbed by thecapacitive impedance 31. As a result, adverse effects of useless noisesand static electricity caused by the presence of the impedances Z1, Z2can be held down at a low level.

[0038] Additionally, in the first example of the structure shown in FIG.3A, when the position at which the vehicle-mounted radio wave radar isattached to the vehicle body is insulated from the body GND 26 by theuse of a resin-made bumper or the like, there is no need of providingthe insulator 30.

[0039]FIG. 3B shows a second example of the structure of thevehicle-mounted radio wave radar.

[0040] In the second example of the structure shown in FIG. 3B, thehigh-frequency circuit section 6 is entirely covered by a metal, andthis metal is connected to a ground line of the high-frequency circuitsection 6. The transmitting antenna 4 and the receiving antenna 5 aremounted on the metal-made antenna base 3. The housing 2 is anelectrically conductive one. The antenna base 3, the control circuitsection 10, and the high-frequency circuit section 6 are arranged in aspace defined by the housing 2 and the antenna base 3. Furthermore, theantenna base 3 is covered by a radome 1. Also, the high-frequencycircuit section 6 is mechanically attached to the antenna base 3 throughan insulator 30.

[0041] The antenna base 3 and the housing 2 are electrically connectedto the body GND 26.

[0042] With the second example of the structure shown in FIG. 3B, thecontrol circuit section 10 and the high-frequency circuit section 6 areelectrically shielded by the ground potential at the body GND 26.However, it is also possible in this case to suppress the generation ofuseless noises and static electricity by determining the position, atwhich the vehicle-mounted radio wave radar is connected to the vehiclebody, so that the impedance (Z1+Z2) between the body GND 26 and thecircuit GND 27 becomes small to such an extent that a potentialdifference Vs produced between the body GND 26 and the circuit GND 27 isnegligible. The radar attachment position satisfying the above conditioncan be determined by measuring an impedance value between the body GND26 and the circuit GND 27 with a tester or the like.

[0043]FIG. 3C shows a third example of the structure of thevehicle-mounted radio wave radar.

[0044] In the third example of the structure shown in FIG. 3C, thetransmitting antenna 4 and the receiving antenna 5 are mounted on themetal-made antenna base 3. The high-frequency circuit section 6 and thecontrol circuit section 10 are arranged in a space defined by theantenna base 3 and an electrically conductive shield case 28. Further,the antenna base 3 and the electrically conductive shield case 28, whichsurround the high-frequency circuit section 6 and the control circuitsection 10 in the space defined by themselves, are arranged in a spacedefined by the radome 1 and the electrically conductive housing 2. Inaddition, the antenna base 3 and the shield case 28 are mechanicallyfixed in place in such a manner that they are electrically isolated fromthe housing 2 by an insulator 30 except for a portion connected to thehousing 2 through capacitive impedance 31 described below.

[0045] The circuit GND 27 common to both the control circuit section 10and the high-frequency circuit section 6 is electrically connected tothe shield case 28, whereas the body GND 26 is electrically connected tothe housing 2. Further, the shield case 28 and the housing 2 areelectrically connected to each other through the capacitive impedance 31in the form of, e.g., a capacitor. A resistance connected to thecapacitor in parallel (for protection of the capacitor) can be providedin a sufficient value by the impedance of the capacitor itself.

[0046] The third example of the structure shown in FIG. 3C is morecomplicated than the first example of the structure shown in FIG. 3A,but can hold down adverse effects of useless noises and staticelectricity caused by the presence of the impedances Z1, Z2 at a lowlevel as with the first example of the structure shown in FIG. 3A.

[0047] A practical example of the structure of the vehicle-mounted radiowave radar according to the embodiment will be described below.

[0048]FIG. 4 is a sectional view of the vehicle-mounted radio wave radaraccording to the embodiment in a state where it is attached to thevehicle body; FIG. 5 is a schematic view, showing another assemblymethod, of the structure of the vehicle-mounted radio wave radaraccording to the embodiment; and FIG. 6 is an external view showing anappearance of the vehicle-mounted radio wave radar according to theembodiment.

[0049] Referring to FIGS. 4 and 5, the high-frequency circuit section 6is mechanically fixed to the antenna base 3. The antenna base 3 is fixedto the housing 2 by, e.g., screws made of conductors. The controlcircuit section 10 comprises a plurality of circuit boards. The circuitboards are stacked in the multilayered form at predetermined intervalstherebetween through spacers 37 to 39, and are arranged between theantenna base 3 and the housing 2. The spacers 37 to 39 are electricallyconductive, and ground lines of the multilayered circuit boards areconnected to each other through the spacers 37-39. Further, in FIGS. 4and 5, a spacer 36 formed of a resilient member, such as rubber or aspring, and having the function of absorbing vibrations is attached tothe spacer 37, which is disposed between the uppermost circuit board andthe antenna base 3, for the purpose of restraining vibrations andabsorbing assembly and dimensional errors. In the assembled state, theantenna base 3 presses the spacer 36 with the function of absorbingvibrations and the spacer 37-39 in a direction in which the circuitboards of the control circuit section 10 are placed in the housing 2.Moreover, the ground lines of the circuit boards of the control circuitsection 10 are electrically connected to ground lines of thehigh-frequency circuit section 6 through the housing 2 and the antennabase 3. The housing 2 is connected to the body GND 26 through capacitiveimpedance 31 in the form of, e.g., a capacitor.

[0050] Additionally, in FIGS. 4 and 5, numeral 43 denotes an O-ring forwater tightness, 33 denotes a packing for water tightness, 32 denotes ascrew, and 34 denotes a waterproof connector.

[0051] Thus, in the vehicle-mounted radio wave radar of this embodiment,the high-frequency circuit section 6, the control circuit section 10,the spacer 36 with the function of absorbing vibrations, and the spacer37-39 are disposed in the space defined by the antenna base 3 and thehousing 2. The control circuit section 10 and the high-frequency circuitsection 6 are hence electrically shielded by the ground potential ofthemselves. Further, in FIGS. 4 and 5, an antenna surface is formed onthe upper side of the antenna base 3 on which the transmitting antenna 4and the receiving antenna 5 are mounted, and the antenna base 3 iscovered by the radome 1. This arrangement protects the transmittingantenna 4 and the receiving antenna 5 from the external physicalenvironment (contamination attributable to moisture, dust, etc.).

[0052] Also, as shown in FIG. 4, the vehicle-mounted radio wave radar ofthis embodiment is attached to a vehicle body 42 through screws 40 andinsulating bushings 41, each of the bushings 41 having a radar-axisadjusting mechanism in the form of a groove structure similar to ascrew. At the same time, the housing 2 and the body GND 26 areelectrically isolated by an insulator 30, which is provided on an outerwall surface of the housing, except for a portion where they areconnected to each other through the capacitive impedance 31, as shown inFIGS. 4 and 6. In this state, the capacitive impedance 31 is connectedin parallel to a certain value of impedance (Z2+Z3) that exists betweenthe housing 2 and the body CND 26. Therefore, noise energy generated bythe certain value of impedance is absorbed by the capacitive impedance31 and reduced. In addition, since the housing 2 and the body CND 26 areshort-circuited in AC fashion, it is possible to avoid the generation ofa noise loop via the vehicle body and to hold useless noises at a lowlevel, which are attributable to the potential difference between thecircuit GND 27 and the body GND 26. As a result, a deterioration of theradar performance caused by adverse effects of useless noises and staticelectricity can be restrained.

[0053] The vehicle-mounted radio wave radar of this embodiment may beassembled as shown in FIG. 5. More specifically, the spacer 36 with thefunction of absorbing vibrations and the spacers 37-39 are prepared asbeing of the press-fitting type. After tentatively assembling thecircuit boards of the control circuit section 10 using the spacers36-39, the circuit boards are inserted downward in the housing 2 withthe aid of a paper tape 35 or the like. Then, the paper tape 35 or thelike is removed and the antenna base 3 is fixed to the housing 2 so asto press the assembled components. By so assembling the radar, thecontrol circuit section 10 can be fixedly disposed within the housing 2without using screws or other any fixtures. Accordingly, the assemblywork is facilitated and the radar size can be easily reduced.

[0054] The housing 2 may be formed of a resin having a surface on whicha metal is coated or plated, or a resin mixed with metallic powder. Inany case, except for the second example of the structure shown in FIG.3B, a portion of the housing, which contacts the vehicle body, iselectrically isolated from the vehicle body. By employing such a resin,the weight of the housing 2 can be reduced while maintaining theelectromagnetic shielding function.

[0055] Furthermore, in the first example of the structure shown in FIG.3A, the housing 2 may comprise an outer layer electrically connected tothe vehicle body when the vehicle-mounted radio wave radar is attachedto the vehicle body, and an inner layer electrically isolated from theouter layer, with the circuit GND 27 connected to only the circuit GND27. Further, one terminal end of the capacitive impedance 31 isconnected to the inner layer of the housing 2, and the other endterminal of the capacitive impedance 31 is connected to the outer layerof the housing 2.

[0056] It is to be noted that electrical isolation between the housing 2and the vehicle body can be realized by any other suitable methods andstructures than those described above.

[0057] According to the vehicle-mounted radio wave radar of the presentinvention, as described above, a deterioration of the radar performancecaused by adverse effects of useless noises and static electricity canbe restrained.

What is claimed is:
 1. A vehicle-mounted radio wave radar, comprising:transmitting/receiving section for transmitting and receiving a radiosignal; signal processing section for processing the radio signaltransmitted and received by said transmitting/receiving section; anelectrically conductive housing for accommodating said signal processingsection therein; an electrically conductive member supporting saidtransmitting/receiving section and disposed so as to close an opening ofsaid electrically conductive housing, and electrically connected to saidelectrically conductive housing; and an insulating member for inhibitingdirect current from passing through said insulating member, wherein saidelectrically conductive housing is connected to a vehicle body throughat least said insulating member, ground of said transmitting/receivingsection and said signal processing section being electrically connectedto at least said electrically conductive housing or said electricallyconductive member.